Within a wireless network, communication is usually effected between so-called base stations and data receivers and transmitters, hereinafter referred to as network terminals. In the case of a mobile radio network, these network terminals are mobile communication terminals (“cellular telephones”), in the case of a WLAN, they are typically mobile computers (“laptops”) with corresponding network interface cards. During data exchange between the base station and a network terminal, radio signals are transmitted, on the one hand, in a so-called “downlink direction” from the base station to the network terminal and, on the other hand, in a so-called “uplink direction”, from the network terminal to the base station. To separate the signal communications in uplink direction and downlink direction from each other, the so-called time-division duplex (TDD) method is used, among others. In the TDD method, the same transmission frequency is used both in uplink and in downlink direction. For an undisturbed signal transmission, a defined time window is allocated to each signal direction, so that transmission is effected alternately in uplink and in downlink direction with a specific clock pulsing. The clock pulsing is usually preset by the base station.
To enable signal transmission even in an area shadowed for radio waves, such as, for example, in a tunnel or inside a building, so-called repeaters are used, which from the point of view of transmission engineering are inserted between the base station and the network terminals. A repeater working according to the TDD method is known, for example, from US 2007/0015462 A1.
In one design, also called distribution system, such a repeater comprises a master unit, communicating in particular with the base station of the radio network, as well as at least one so-called “remote unit”, which—arranged, for example, inside the building—established the contact with the network terminal. The signal transmission between the master unit and the remote unit is often effected in the form of an optical communication signal through an optical waveguide, for example a fiber optic cable.
The master unit forwards the signal received from the base station in the downlink direction to the remote unit. Vice versa, the remote unit forwards a signal arriving from the mobile-communication terminal in the uplink direction to the master unit. Often, the signals in uplink and in downlink direction are transmitted through a common waveguide.
To use such a repeater within the framework of a TDD signal transmission, the signal transmission through the waveguide must be adapted to the preset clock pulsing of the surrounding radio-signal transmission. In particular, the master unit and the remote unit have to be synchronized with each other in conformity with the clock pulsing.